In a so-called by-wire brake that is used as a vehicle brake system, for example, there has been known to use a brushless motor as a servo motor for a driving source. In such a motor, when a high brake pressure is requested by driver's operation of a brake pedal such that a current supply more than a current capable of continuous energization of the motor is required, the motor becomes hot in some cases. To solve this problem, in Patent Document 1, there is disclosed a technology of reducing a current supplied to the motor for generating a braking force, when generation of the braking force has continued for a predetermined period of time or more.